Semen (from the Latin word for "seed") is the whitish fluid that a male ejaculates from his penis. The slang word for that is "cum" or "come".
Some people call this the sperm, but that is only part of it. Sperm are only about 2 to 5% of the volume of the semen and are created in small coiled tubes in the testicles (or "testes") at the rate of about 100 million a day and they are the cell which fertilises the female egg (the proper name is "ovum"). However the sperm cells only are only up to about 5% of the semen. About 65% of the semen volume comes from the seminal vesicles and 25% from the prostate gland. Where is the other 5%? These figures are approximate and can vary a bit.
The semen (or "seminal fluid") also contains nutrition in the form of fructose sugars that provide nutrition for the sperm cells as they travel up the vagina towards the cervix until they reach any egg that is present. Semen also helps to transport the sperm in this trip.
